Reference (1) includes a discussion of the broad reach of fiber optical communications systems into the modern world and the specific need to monitor individual fiber optic links in these systems for fiber breakage so that failed links may be quickly be identified and automatically corrected by quickly switching a spare optical fiber into service. The inventive contribution made in Reverence (1) was a cost effective optical switching apparatus that could sequentially direct tapped optical signals from fiber optic transmission links to monitoring equipment that could detect fiber breaks in several seconds or less. This same switching apparatus could also be used to replicate optical signals for broadcast and multimedia applications.
In many cases, there is a need not only to monitor optical fibers used in modern communication systems for continuity (lack of breaks) but also to monitor the performance of each of a multiplicity of optical channels carried by each individual fiber in a wavelength division multiplexed (WDM) format. For example, it is important to detect and identify when a laser diode that serves as the optical source for one of many WDM channels on a fiber has failed or is approaching failure due to a declining power output.
WDM is a well established method for increasing the information carrying capacity of individual fibers. Depending on the system application, the number of optical channels that are wavelength division multiplexed range from several channels, referred to as Coarse WDM (or CWDM), to 160 channels or more, referred to as Dense WDM (or DWDM). In either case, WDM leads to a beneficial reduction in the total number of optical fibers required to convey some specified amount of information or data. However, in order for WDM to be a cost effective strategy, the cost for monitoring the individual channels multiplexed onto a fiber must be reasonably modest. While the state-of-the-art for monitoring has reached this threshold using MEMS technology previously discussed in Reference (1), further improvements to reduce the complexity and expense of the monitoring function would be welcomed.
The state-of-the-art for channel monitoring is to direct the output of a WDM optical fiber into a dispersive Planar Lightwave Circuit (PLC) such as an Arrayed Waveguide Grating (AWG), that is well known in the art, to split up a multiplicity of WDM channels (say, N channels) carried on a single input fiber into a group of single channels carried on a multiplicity N of individual output fibers with one channel on each fiber. Then, an optical switch, similar to the MEMS switch described in Reference (1), is used to sequentially direct the channel outputs to an optical monitoring device (test set).
Clearly, it would be desirable to make this switching function more cost effective. It would also be desirable if this cost effective alternative switching apparatus could also be used for other applications such as optical signal replication.
Also see U.S. Pat. No. 7,330,620 B2 and, U.S. Patent Application Publication Nos. 2009/0232447 A1. 2012/0087668 A1, and 2012/0230690 A1.